Various types of hearing prostheses provide persons with different types of hearing loss with the ability to perceive sound. Hearing loss may be conductive, sensorineural, or some combination of both conductive and sensorineural. Conductive hearing loss typically results from a dysfunction in any of the mechanisms that ordinarily conduct sound waves through the outer ear, the eardrum, or the bones of the middle ear. Sensorineural hearing loss typically results from a dysfunction in the inner ear, including the cochlea where sound vibrations are converted into neural signals, or any other part of the ear, auditory nerve, or brain that may process the neural signals.
Persons with some forms of conductive hearing loss may benefit from hearing prostheses such as acoustic hearing aids or vibration-based hearing devices. An acoustic hearing aid typically includes a small microphone to detect sound, an amplifier to amplify certain portions of the detected sound, and a small speaker to transmit the amplified sounds into the person's ear. Vibration-based hearing devices typically include a small microphone to detect sound and a vibration mechanism to apply vibrations corresponding to the detected sound directly or indirectly to a person's bone or teeth, thereby causing vibrations in the person's inner ear and bypassing the person's auditory canal and middle ear. Vibration-based hearing devices include, for example, bone anchored devices, direct acoustic cochlear stimulation devices, or other vibration-based devices. A bone-anchored device typically utilizes a surgically implanted mechanism or a passive connection through the skin or teeth to transmit vibrations corresponding to sound via the skull. A direct acoustic cochlear stimulation device also typically utilizes a surgically implanted mechanism to transmit vibrations corresponding to sound, but bypasses the skull and more directly stimulates the inner ear. Other non-surgical vibration-based hearing devices may use similar vibration mechanisms to transmit sound via direct or indirect vibration of teeth or other cranial or facial bones or structures.
Persons with certain forms of sensorineural hearing loss may benefit from implanted prostheses such as cochlear implants and/or auditory brainstem implants. For example, cochlear implants can provide a person having sensorineural hearing loss with the ability to perceive sound by stimulating the person's auditory nerve via an array of electrodes implanted in the person's cochlea. A component of the cochlear implant detects sound waves, which are converted into a series of electrical stimulation signals that are delivered to the implant recipient's cochlea via the array of electrodes. Auditory brainstem implants can use technology similar to cochlear implants, but instead of applying electrical stimulation to a person's cochlea, auditory brainstem implants apply electrical stimulation directly to a person's brain stem, bypassing the cochlea altogether. Electrically stimulating auditory nerves in a cochlea with a cochlear implant or electrically stimulating a brainstem may enable persons with sensorineural hearing loss to perceive sound. Further, some persons may benefit from hearing prostheses that combine one or more characteristics of acoustic hearing aids, vibration-based hearing devices, cochlear implants, and auditory brainstem implants to enable the person to perceive sound.
Some hearing prostheses include separate units or elements that function together to enable the person to perceive sound. In one example, a hearing prosthesis includes a first element that is generally external to the person and a second element that can be implanted in the person. In the present example, the first element is configured to detect sound, to encode the detected sound as acoustic signals, to deliver the acoustic signals to the second element over a coupling or link between the first and second elements, and/or to deliver power to the second element over the link. The second element is configured to apply the delivered acoustic signals as output signals to the person's hearing system and/or to apply the delivered power to one or more components of the second element. The output signals applied to the person's hearing system can include, for example, audible signals, vibrations, and electrical signals, as described generally above.
The coupling or link between the first and second elements can be a radio frequency (RF) link operating in the magnetic or electric near-field, for example, and can be utilized to operate the hearing prosthesis in one or more modes, such as applying output signals to the person's hearing system and charging a power supply of the hearing prosthesis. In general, different operating modes of the hearing prosthesis may represent different load conditions that affect the efficiency of the coupling between the first and second elements. In various examples, the efficiency of the coupling can be optimized for a load condition of a particular operating mode or optimized for an average load condition of a plurality of operating modes, which results in a compromise design of the hearing prosthesis. Generally, it is desirable to improve on the arrangements of the prior art or at least to provide one or more useful alternatives.